Improve raw noise model for N5.
Improve raw noise model for N5.

Replace the current raw noise model, calibrated using Android's
dng_noise_model.py script, with an improved noise model, using an
updated version of that script.

The new raw noise model has a different parameterization in terms
of ISO:

- The formula for 'S' scales with ISO. While shot noise should
  be zero for a completely dark signal, we still include an offset
  here to help compensate for black level variations with ISO.

- The new formula for 'O' scales with ISO^2, not ISO. This form is
  required because 'O' corresponds to the *variance* due to read
  noise. The new formula also treats analog and digital gain
  separately. While pre-ADC read noise is affected by both types
  of gain, post-ADC read noise is affected *only* by digital gain.

Bug: 16273313
Change-Id: If7d1e48138230a487a5b270e5686c699e80ff419

maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead,maruos/android_device_lge_hammerhead